DESCRIPTION

checks for an alphanumeric character; it is equivalent to
(isalpha(c) || isdigit(c))fR.

isalpha()

checks for an alphabetic character; in the standard fB"C"fP
locale, it is equivalent to
(isupper(c) || islower(c))fR.
In some locales, there may be additional characters for which
isalpha()
is true--letters which are neither upper case nor lower
case.